This invention relates to pneumatic radial ply tires and the interrelationship between the tire and its design rim.
Historically, with the introduction of the tubeless type tire, the design fitment of the bead portions of the tire to the design rim has increased in significance. This fitment insures that the tire remains air tightly sealed and securely fixed to the rim during vehicle use.
The typical rim has a bead seat and a rim flange that defines the contact zone with the tire bead. The tire bead has an annular surface between the bead heel and bead toe that upon assembly to the rim contacts the bead seat. The bead-also has an annular surface radially outwardly of the bead heel, this annular surface contacts the rim flange when the tire is mounted and inflated on the rim.
The prior art teaches the use of a rim with cylindrical or very slightly conical bead seats. Typically such bead seats were inclined at an angle of 5.degree. relative to the axis of rotation of the tire. To ensure a proper fitment, the tire beads had an annular surface having a similar 5.degree. inclination relative to the axis of rotation, the beads having a slightly smaller diameter than the rim seat, thus upon assembly, a snug interference fit would be achieved. Such a prior art tire is shown in FIG. 3A.
As a later development, the radially innermost flexible toe portion of the tire between the toe and the annular tensile member comprised an inclined surface about 5.degree. greater than the rim seat. This added interference created by the angular variation facilitated sealing the tire. This prior art tire is illustrated in FIGS. 3B and 3C.
The prior art tires had beads with a surface radially outwardly of the bead heel. This surface ideally should contact the rim flange, both the rim flange and this axially and radially outwardly surface being oriented at 90.degree. relative to the wheel axis. This area being under pressure while the tire is inflated over a portion of its surface, contacts the rim flange essentially fastenings the tire on the rim.
The prior art tires essentially relied on the rim seat and flange orientation to establish the shape and orientation of the bead, with the exception being the flexible toe portion of the bead.
Surprisingly it has been discovered that the prior art tire bead designs have a less than ideal fitment to the rim, particularly in the rim flange area of the J type rims. Those skilled in the art have believed that the surface radially outward of the bead heel was in firm surface contact with the rim flange. In fact, tangential x-rays indicate that a portion of this flange surface area is actually spaced from the rim creating a gap and, therefore, is of no assistance in firmly fixing the tire to the rim.
It has been discovered that a tire made according to the present invention, having unique bead surfaces for contacting the rim can result in a tire having improved lower sidewall stiffness, better rolling resistance and improved comfort. A tire made according to the present invention can exhibit uniformly low bead seating forces when mounted to the rim, yet also exhibit superior adhesion of the tire to the rim.